Digital images obtained by image acquisition devices such as a digital camera are stored in a storage space, e.g., a non-volatile memory such as EEPROM, a memory card comprised of SDRAM, and backup battery. The storage space is so limited that if the acquired images exceed a predetermined amount, additional images cannot be stored until the previously stored images are erased.
In order to save as many images as possible in a limited storage space, the image captured must undergo data conversion and compression processes before being stored in a memory card. In this case, the size of stored image can vary depending on its resolution and compression ratio.
However, an increase in compression ratio increases the memory size but results in loss of data compared to the original image. Thus, as the compression ratio increases, it is more unlikely to faithfully restore the original image when recovering the compressed image data for display on a display screen.
To troubleshoot this problem, a typical digital camera is designed for a user to set the resolution and compression ratio according to the number of images that can be stored in a limited storage space as well as the desired image quality.
Japanese Patent Publication No. Hei 8-262746 discloses a digital camera designed for a user to set and change the compression ratio of image data and indicate the number of remaining images yet to be photographed according to the changed compression ratio.
One conventional approach which changes the number of additional images that can be photographed if a storage space is not enough is for the user to directly adjust the resolution or compression ratio of an image through a menu or button. However, this method has a problem of not acquiring an image when it is needed immediately. Another approach involves temporarily storing a captured image in a temporary storage device such as an integrated circuit (IC) memory, reducing the amount of image data in the IC memory, and saving the image on a storage device. However, it also has the drawback of requiring a great deal of time in photographing an image.